Like many of the things I make, this is a very randomly-assembled concoction and my measurements are not exact. I'm posting it, though, because it turned out surprisingly good and it might give people with limiting diets ideas for their own desserts.
So the Betty Crocker Gluten-Free Mixes are the best IMO - and I've tried quite a few different ones over the years - but everything has a down side. While the texture is perfect straight out of the oven, if you don't eat the chocolate chips and brownies very quickly, they get hard and crunchy. Something I've also noticed, though, is that the only GF baked good I've ever seen go mouldy is bread. And that's not even all types of bread; it's mostly the homemade kind. I'm sure various cakes and things will go mouldy if you give them the chance, too, but the overwhelming majority don't really seem to go bad. Stale and a little off-tasting after a long time, sure, but not bad.
So anyway, I didn't get a chance to ear like 2/3 of a batch of Betty Crocker chocolate chip cookies one time, but went ahead and stashed them in a Ziploc bag in the cupboard even though I knew they'd gone a bit hard. A while later, I didn't get a chance to eat about half a batch of the brownies.I went ahead and stuck these in with the cookies, which had broken a little and broke even more when I accidentally dropped them. They pretty old by perishable food standards but still tasted the same. So, you know, I figured I should finish crushing them all up and use the crumbs in another dessert.
Ideally you'll want to use fewer crumbs than I did. As I said, there were quite a few cookies and brownies I didn't get a chance to eat. Using just under half of a gallon Ziploc bag full (once they're thoroughly crushed of course) and 1/2 a cup of butter should be just right.
To replicate what I made, you'll need:
A tart pan
3/4 of a gallon Ziploc bag of mixed chocolate chip and brownie crumbs
3/4 cup of butter
2 cups milk
2 boxes of Dr. Oetker's Mousse Supreme, one French Vanilla, one White Chocolate
One package strawberries
Approx. 2 tablespoons almond-flavoured chocolate frosting
Approx. 3 tablespoons of Nutella
Dr. Oetker's Mousse Supreme is an import that came from an Asian market that also had European groceries. The finished product, as you can guess, is a lot like a light vanilla pudding, so I'm sure there are plenty of substitutes available.
You might be wondering about the almond chocolate frosting, too. It was a standard can of Chocolate Fudge-flavoured frosting plus a little flavouring packet I found at Wal-Mart. It tasted kind of like marzipan and gave the GF cake I'd frosted with it a nice hint of grenadine.
So anyway, pour your bag of thoroughly-crushed crunchies into a mixing bowl. Melt the butter, drizzle it over the crumbs, and fold it all together with a spatula or spoon. When thoroughly mixed, pour it into the tart pan and press it in as well as possible with your fist or another implement.
Next, I mixed the remaining flavoured frosting together with what little Nutella I'd had left and spread it over the crumbs. There was just enough for a very thin layer.
Now follow the instructions on the mousse box, or for whatever filling you're using. Whipped cream would be nice to put on top but isn't enough for this FrankenTreat on its own, so you'll have to find something richer and thicker. In this case, you needed one cup of milk for each box of mousse, to be blended with the mix at high speed. When ready, simply spread the mousse over the crumb base and chill for at least two hours before serving.
I served mine with sliced strawberries on top, though I'm sure it'd also be good with the aforementioned whipped cream, mixed summer berries, mandarin oranges, shredded coconut, cherry pie filling, caramel, et cetera. The possibilities are endless. I really hope someone else finds this to be a good use for the incredibly specific niche problem of overly crunchy GF baked goods :D